Subterranean explosives have been used for many years for geological mapping and exploratory efforts and for activating or rejuvenating relatively dormant subterranean deposits of petroleum, gas, water or steam. Typically, a gaseous, solid, or liquid explosive charge medium was pumped down a well casing and permeated the earth structure in the vicinity of the end of the casing which may have been several thousands of feet below the surface. A detonating device was then located in the gaseous or liquid explosive medium or environment and initiated by remote wire or timer control. To protect the well casing from damage from the ensuing explosion, a plug was placed in the casing above the charge to limit the charge from propagating upward from the lower end of the well casing. Above the plug, concrete, liquid or other suitable tamping material was used. The charge was exploded from the surface electrically via wires connecting the detonator below to the surface.
But the use of wires to initiate detonation created problems of reliability because the wiper plug and tamping obstruction was in the way for the wires. Also, the substantial depths necessary for proper placement of the detonators to which the wires had to be connected caused difficulties in placing the wires. This had led to the use of timers in the detonators to avoid the necessity for providing the electrical wires. However, timers did not eliminate safety problems against accidental detonation and it introduced reliability problems due to failures in the timer mechanisms. This system also lacked flexibility in that the timer had to be set long enough to allow for time delays in placement of the detonator and tamping plug while, if there were no undue delays, the operators had to wait the full term of the timer before detonation, even though all preparations for the explosion may have been completed for some time.